Klass.Nr: A6001
Volume Deficits of Non-Ferrous Metal Castings
Contents
P 201 May 2002
Page
1 1.1 1.2 1.3 2 2.1 2.1.1 2.1.2 2.2 3 3.1 3.2 3.3 3.4 4 5 5.1 5.1.1 5.1.2 5.1.3 5.1.4 5.2 5.2.1 5.2.2 5.2.3 5.2.4 5.2.5 5.2.6 6 6.1 6.2 7
Scope General Alloys Casting processes Explanatory notes Porosity Shrinkage cavities Gas porosity Other flaws Possible effects of porosity Static strength Dynamic strength General leak tightness and mating surfaces Surface and heat treatment Evaluation of casting porosity Description of porosity Pore classes Pore class designation Reference surfaces for the pore classes Porosity class determination Examples for pore class designations Test options Radiography test with image intensifier Ultrasonic test Leak tightness test Visual test Density test Metallographic test and section test Drawing notes Collective notes Notes for defined areas References, standards, guidelines
2 2 2 2 2 2 2 3 3 3 3 4 4 4 4 5 5 5 6 7 7 8 8 8 8 9 9 9 9 9 9 10
Annex 1 Annex 1.1 Annex 1.2 Annex 1.3 Annex 1.4 Annex 1.5 Annex 1.6 Annex 2 Annex 3
Definition of further flaws Cold flow marks Build-up (stick marks) Draw marks Burrs Hot cracks Further characteristics of cast components Microstructure examples of pore classes 0, 4 and 8 Examples of different porosity in general and in dependence on the reference surfaces (informative)
12 12 12 12 12 12 12 13 14
Specification by the Special Technical Committees Die Casting and Light Metal Casting of the German Foundrymen’s Association (VDG)
VEREIN DEUTSCHER GIESSEREIFACHLEUTE To be obtained from VDG-Informationszentrum Giesserei, Postfach 10 51 44, D-40042 Düsseldorf, Telefon (02 11) 68 71-254 To be quoted only with permission of the German Foundrymen’s Association
Page 1, VDG Specification P 201
revised and updated 2002-10-16
QUELLE: NOLIS (Norm vor Anwendung auf Aktualität prüfen!/Check standard for current issue prior to usage)
The English translation is believed to be accurate. In case of discrepancies the German version shall govern.
VDG SPECIFICATION
Scope
1.1 General This VDG specification applies to non-ferrous metal castings. It aims at a description of casting quality requirements as well as their uniform presentation in technical documentation. The scope of this specification is restricted to inner and outer volume deficits (porosity). Other flaws such as sink marks, cold flow marks, build-up, draw marks, burrs and hot cracks are not subject of this specification. Porosity can be minimised if designer and caster collaborate.
1.2 Alloys The scope of this specification is restricted to aluminium, magnesium and zinc base alloy castings acc. to the relevant standards (DIN EN 1706 "Aluminium“, DIN EN 1753 "Magnesium“, DIN EN 12844 "Zinc“).
1.3 Casting processes This VDG specification is restricted to die casting including related special casting processes, such as squeeze casting and thixocasting, as well as to sand casting and ingot casting procedures.
2
Explanatory notes
2.1 Porosity 2.1.1 Shrinkage cavities Shrinkage cavities result from the thermophysical properties of the cast materials during solidification. It is impossible to manufacture castings free of shrinkage cavities. Metallic materials in liquid and solid aggregate state have different densities and therefore different specific volumes. The transition from liquid to solid state causes a change in volume (Figure 1). For commonly used nonferrous metal alloys, their volume decreases during cooling (volume deficits, solidification contraction).
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Fluid contraction
Specific volume, cm3/g
1
Solidification contraction
Solid contraction TM
Temperature, °C TM = Melting point
Figure 1 Specific volume of aluminium depending on temperature As generally outer shell and sprue of a part solidify early, a volume deficit occurs in the casting. This causes cavities in the casting. By means of a suitable design of the casting, e.g. avoidance of differences in the wall thickness, and optimum design of the casting system, this volume deficit can be minimised. Shrinkage cavities are hollow and have a more or less rugged shape. In case the outer shell cannot withstand the stresses which occur during shrinkage, this may result in shrinkage cracks or hot cracks. If casting and mould are designed in an appropriate way, these cracks and cavities can be cured by refeeding the affected areas. Alloys with a wide solidification interval are especially sensitive to hot cracks. If cavities and pores can be observed with the emmetropic eye, this is called macroporosity, if not, it is called microporosity. 2.1.2 Gas porosity Gas pores can have: – –
Thermodynamic causes Fluidic causes
2.1.2.1 Thermodynamically caused gas porosity In liquid metals elementary gases generally are better soluble than in solid metals. Therefore gases are exuded during solidification, which leads to pore formation.
The pores accumulate remaining solidification.
in
the
area
of
In alloys with a distinct solidification interval, gas exudation preferably takes place between the dendrite arms. As a result, gas pores caused by exudation generally do not have a round contour. The contour rounding depends on the gas content of the melt. 2.1.2.2 Gas porosity caused by fluidics During mould filling, gases are included as a result of metal flow. These gases are either gases from the ambient air or gases that result from the thermal contact reaction between the melt and the moulding material or the material of the casting mould and/or accessory casting materials such as release agents, die lubricants etc. Gas pores caused by fluidics generally are round as a result of transitional stresses between gas and melt. Note: In general, both types, shrinkage cavities and gas pores occur in combination.
2.2 Other flaws In addition to porosity other flaws may occur which can influence the casting quality, such as cold flow marks, built-up, draw marks, burrs and hot cracks. These flaws are mentioned in this specification and defined in Annex 1; however they are not subject of this specification. As far as possible, reference is made to other guidelines and standards that refer to these flaws and their test methods.
3
Possible effects of porosity
According to type and properties of the component as well as to load case, pores in castings can affect strength, leak tightness under pressure, surface characteristics and/or appearance of the component. In the case of technical grade components special attention shall be paid to the effects of porosity on component strength. The same porosity can have different effects on statically and dynamically stressed components.
In both cases points of force application, stress intensity and areas of stress concentration should be given in order to ensure suitable selection of pore classes.
3.1 Static strength When a force is applied to a component, this causes stress in the cross section under load. This stress is proportional to the quotient of force and cross sectional area. If the cross section is minimised (weakened) because of pores, the stress increases. As soon as the resulting stress exceeds the elastic limit of the material, permanent deformation occurs which can lead to fracture. In addition to this increase in stress caused by the crosssectional minimisation, a notch effect arises, depending on pore geometry. The most critical aspect in the case of static stress is the portion of pores related to the cross sectional area and therefore the weakening of the cross section . Under bending stress and torsional stress, the position of porosity in relation to the neutral fibre is to be observed. Especially in the case of shrinkage pores, porosity is located in the excess material area and therefore near the neutral fibre. As a result, strength reduction in the total cross section is proportional to the surface portion of porosity in good approximation.
3.2 Dynamic strength Concerning the dynamic strength of a component, besides the material the notch effect is of great importance. Geometric contours, inhomogeneity caused by oxide films, inclusions, microstructure components, intermetallic compounds etc., and casting defects can lead to notches having a more serious effect than pores. Depending on their shape, their position relative to the casting surface and their arrangement, pores have different notch effects. The notch effect – Increases with the area occupied by porosity and the pore diameter – Decreases with better roundness and greater distance of the pores from the casting surface
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Examinations concerning the fatigue strength of aluminium cast alloys have revealed a decrease of the fatigue strength by approx. 15 to 20 % [1 to 11], when the porosity is increased from pore class 0 to pore class 8 (see figure in Annex 2 [12]).
3.3 General leak tightness and mating surfaces When gas pores, shrinkage cavities and hot cracks are directly connected with the casting skin (open pores, sink marks) or when they are cut during machining, this may lead to leakage of the components or mating surfaces depending on pore distribution. In connection with the requirement for leak tightness under pressure, especially hot cracks and interconnected cavities are to be considered as critical. Depending on their shape and size, pores can cause damage and/or impairment of seals.
3.4 Surface and heat treatment If the components have been coated, electroplated or heat treated, surface porosity can cause points of discontinuity and/or surface blisters. During heat treatment (annealing, thermal drying of paints, etc.) of castings, the elevated temperature causes a strength reduction of the material. As a result, the internal pressure causes deformation and/or blistering, especially of gas-filled pores. This applies in particular to die cast components (see 2.1.2.2). Even in die casting, blistering can be prevented to a great extent by applying forced ventilation to the die.
4
Evaluation of casting porosity
The degree of porosity depends on the material, the manufacturing process, the process-compatible design of the component, its function and the permissible degree of porosity. In general, it can be noted that an enhancement of the porosity requirement leads to increased efforts for production and testing, and therefore to increased costs.
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Two types of distinguished: microporosity:
porosity have macroporosity
to
be and
Macroporosity includes all pores, the size and shape of which can be specified with the emmetropic human eye or an auxiliary means with the same resolution (such as X-ray method). This applies to pores with a minimum extension of 0.5 mm. Microporosity includes all pores, the shape and size of which cannot be reliably evaluated with the naked eye. This includes pores up to a maximum diameter of 0.5 mm. The minimum pore size to be determined depends on the resolution of the auxiliary means used. Porosity requirements shall be guided by the component requirements (static strength, fatigue strength, leak tightness under pressure and function of machined surfaces, appearance of unfinished casting surfaces). Evaluation criteria and measures shall be defined by manufacturer and customer by the time of ordering. Area-specific criteria should be explicitly defined on one component (see 5.1). Publications [12 to 19] can help defining evaluation criteria and measures.
5
Description of porosity
5.1 Pore classes In order to describe all porosity requirements of a component, different pore classes can be defined for sub-areas of the component. Experience shows that it is difficult to manufacture complex components in only one pore class. 5.1.1 Pore class designation The pore class designation consists of the following parameters: Load case: The load case parameter can be designated as follows: S for components under static stress mainly D for components under dynamic stress mainly F for components with special requirements on functional surfaces
G for components without further specified requirements
–
Porosity: The porosity parameter for the surfaces agreed upon states the maximum permissible porosity in percent for the load cases G, S and D, and the maximum permissible number of defined pores related to a reference surface for the load case F. The reference surface is always square, triangular (isosceles) or round, with its shape depending on the respective component geometry (see Figure 2 and 5.1.2).
–
Diameter: The specification of the diameter parameter is optional. It specifies the maximum permissible comparison diameter of single pores. Optionally, manufacturer and customer can agree on the mean length or on the mean pore diameter or on the equivalent diameter. (The comparison diameter is the smallest diameter possible including all pores; the equivalent diameter is the diameter of a circle of the same area.) Additional parameters: The specification of the additional parameters Z1 to Zn (from German "Zusatz") is optional. They can be used separately or in multiple combinations and assume the following values: An
M
Distance between adjacent pores. This parameter specifies the minimum edge distance between two adjacent pores. The minimum edge distance is the diameter of the smaller one of two adjacent pores multiplied by the factor n in mm. (A = distance; from German "Abstand") The value for n shall be agreed upon by manufacturer and customer. Centre of the component wall. This parameter can only be used in connection with the diameter parameter. Localised porosity is only permissible in the centre (M; from German "Mitte") of the component wall. Localised porosity is an accumulation of single pores. Necessary prerequisites for the presence of localised porosity are:
The localised porosity diameter is greater than the maximum permissible size of single pores. The distance between adjacent pores is smaller than the diameter of the smallest of these pores.
C
Excess material. This parameter can only be used in connection with the diameter parameter. Localised porosity is only permissible in excess material and joint areas (heat centres = C).
R
Component wall centre area. The parameter R is only permissible for pore classes D10 to D30. (e.g. D10: mainly dynamically stressed with a maximum permissible porosity of 10 %) The specified porosity class only applies to the centre area (R) of the component wall (inner third of the relevant wall thickness). In the two outer thirds porosity class D4 shall be adhered to.
Pn
Pore size. This parameter can only be used in connection with the diameter parameter. The maximum permissible pore size (defined by the diameter parameter) only applies to the component wall centre area (inner third of the relevant wall thickness). In the two outer thirds the maximum permissible pore size (P) of single pores is limited to a diameter of n mm. In pore class F, n specifies the diameter up to which pores are not considered.
Representation: (load case)(porosity)/ [diameter]/[add. parameter 1]/ [...] /[add. parameter n] e.g. S5/2/C or F4/3/A0.5/P0.8 In order to describe the permissible pore class sufficiently, at least the parameters in round brackets are to be specified. The parameters in square brackets are optional. 5.1.2 Reference surfaces for the pore classes When the component is cut in view – for pore class F the functional surface is considered – this results in an area which can be divided in squares, triangles (e.g. isosceles) or circles. The respective reference surfaces of these
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sub-areas shall be chosen in such a way that they cover a maximum surface and fit the outer contours of the sub-areas (Figure 2)1. Around bores and threads the reference surface is the largest ring area around the bore/thread, if the bore/thread is cut at right angles to the longitudinal axis. In this case, the thickness of the ring is considered as a common wall thickness. In addition, the following is required for pore classes D1 to D4: In none of the sub-areas of the respective reference surface (sub-area with optional location within the reference surface, dimension of the sub-area = 3 mm x 4 mm), the portion of surface porosity may exceed 4 % (in addition to correspondence with the class-specific porosity). This is not required if the reference surface is too small. Pore classes D1 to D4 should only be used in especially critical component areas and in exceptional cases (see also 5.2). For all other areas pore classes D5 and higher are recommended.
Reference surfaces Sub-area of reference surface
5.1.3
Porosity class determination
The determination of porosity classes according to this specification entails costs for mandatory testing which have to be assessed. 5.1.3.1 Pore class S (for static stress) Specimen preparation as well as the optical resolution used for porosity testing of pore class S shall be agreed upon between caster and customer. Agreements should preferably be documented in the corresponding component drawings or in a test specification. In case of doubt, class S porosity shall be evaluated on a plane surface with a medium peak-to-valley roughness of at least Rz 25, and a resolution corresponding to that of the naked human eye. 5.1.3.2 Pore class D (for dynamic stress) If not otherwise agreed upon between caster and customer, for a porosity specification of class D, porosity is always evaluated on a metallographic microsection with a magnification of 25 : 1 or 20 : 1 under a microscope. Porosity classes D1 to D4 are exclusively evaluated on a metallographic microsection with a magnification of 25 : 1 or 20 : 1. If no special testing cross section is specified in the component drawing, the specification applies to all cross sections of the respective component.
5.1.3.3 Pore class F (special requirements on functional surfaces) Sub-area of the component section
Figure 2
Section of a component with pores and respective reference surfaces for porosity determination (see also examples in Annex 3)
1
Rectangular reference surfaces are permissible if agreed upon by manufacturer and customer.
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If not otherwise agreed upon between manufacturer and customer, the porosity of this pore class is evaluated with the naked eye on the finished functional surfaces. 5.1.3.4 Pore class G (components without further specified requirements) If not otherwise agreed upon between manufacturer and customer, the porosity of this pore class is evaluated with X-rays on a system with a focal spot ≤ 1 mm. The generated X-ray image is evaluated as a two-
dimensional cut surface of a component and divided into reference surfaces acc. to 5.1.2. If not otherwise agreed upon between manufacturer and customer, the reference surfaces selected this way shall not exceed 5 cm2, with observance of the ratio Xray : casting = 1 : 1. In the case of deviating ratios the maximum size of the reference surface shall be adapted accordingly. 5.1.4
Examples for pore class designations
Example 1: General designation
add. parameter n add. parameter 2 add. parameter 1 pore diameter porosity
For a casting the general porosity specification S5/2/C is noted in the drawing. Furthermore, the additional parameters F4/3/A0.5/P0.8 acc. to the drawing apply to one of the three functional surfaces of this casting. This specification means: A maximum permissible porosity of ≤ 5 % applies to the whole statically stressed component. In the component, single pores up to a maximum diameter of 2 mm are permissible. Localised porosity is only permissible in excess material and joint areas (heat centres) (example 2). In the specific functional surface a maximum of 4 defined pores per reference surface are permissible. The maximum permissible single pore diameter is 3 mm, the minimum edge distance of the pores to each other is 0.5 x diameter of the smallest of two adjacent pores. Single pores up to a diameter of 0.8 mm are not considered (example 3).
load case
5.2 Test options Example 2: Designation S5/2/C
Localised porosity in joint area and access material permissible max. permissible pore diameter: 2 mm max. permissible porosity: 5 % mainly static ally stressed
Example 3: Component with special requirements F4/3/a 0.5/P 0.8
Pores up to a diameter of 0.8 mm not considered Minimum distance betw een tw o pores: 0.5 x ∅ of the smaller pore Per missible single pore diameter: 3 mm Max. four defined pores per reference surface Component w ith special functional surface requir ements
For evaluating the porosity of castings, various test methods can be used. The test method should be specified between manufacturer and customer in connection with the specification of evaluation criteria while taking into consideration the component requirements. [1] 5.2.1 Radiographic test with image intensifier (RT)The radiography test (Xray test) [2, 3, 4, 5] is a nondestructive test. The resolution of this test method depends on the wall thicknesses to be tested, the distance and angle of radiography and the casting geometry. In the X-ray test a two-dimensional projection of the casting is created. This causes problems in pore localisation and identification. The maximum resolution of standard X-ray systems used in foundries is approx. 0.5 mm. 5.2.2 Ultrasonic test (UT) The ultrasonic test is a nondestructive test [6]. The resolution depends on the casting contour of the wall thicknesses to be tested as well as on the ultrasonic distance and angle. In the ultrasonic test a one-dimensional projection of the casting is created. A total overview of a
Page 7, VDG SpecificationP 201
5.2.3 Leak tightness test (LT)
ground surface, on a milled or turned surface or on a polished microsection. The resolution of this method depends on the appearance of the considered surface and on the auxiliary means used for evaluation. The metallographic test and section test only allow an evaluation of porosity in the considered section plane. Therefore, this test is only suitable for increased requirements in critical component areas.
The leak tightness test is a nondestructive test [7, 8]. It is applied when leak tightness under pressure is required for a casting . The leak tightness test only makes sense if special requirements for the leak tightness of a component are evident.
The metallographic test is the method providing the highest level of information concerning critical component areas, as it gives the most detailed information on the causes and origins of porosity and further influences on microstructure.
5.2.4 Visual test (VT)
This test method is very complex and therefore cost-intensive; it requires especially careful execution [20, 21].
component can only be generated by scanning the entire component. During ultrasonic testing, complications can occur when the transducer is coupled and when the reflected signals (determination of size, number and position of pores) are evaluated. Therefore, this porosity specification method is only applicable in special cases.
The visual test is a nondestructive test. Its resolution depends on the test equipment used (e.g. magnifying glass) [10]. The visual test is performed on the rough contour of the casting or on machined surfaces. A quantification of general porosity is not possible using this test method. Specialised staff is required for the following nondestructive test methods: RT (Radiographic Testing) UT (Ultrasonic Testing) LT (Leak Tightness Testing) VT (Visual Testing) 5.2.5 Density test The density test is a nondestructive test. This method only allows the identification of the portion of volume porosity in the entire component. Pore size and location can only be determined for single segments by cutting (destroying) the castings. As in general the density test is performed with water according to Archimedes' Principle, this method does not allow a quantification of open pores. The density test in general is suitable as an auxiliary means for production optimisation. 5.2.6 Metallographic test and section test The metallographic test and the section test are destructive tests. They can only be performed on random samples. Evaluation is performed on a saw section, on a coarsely
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The fact that pores might be filled by excess material due to grinding, cutting or polishing has to be observed. This can lead to misinterpretation.
6.
Drawing notes
In drawings, pore classes are to be specified according to 5.1 for the entire component or for special areas.
6.1 Collective notes According to this specification, collective notes of the maximum permissible porosity in % are possible for the load cases S, D and G defined in 5.1.1. For pore classes D1 to D4, collective notes are not permissible. A collective drawing note shall be situated near the title block, with the specifications of load case and maximum permissible porosity being mandatory. Porosity acc. to VDG specification P201 (see 5.1.4): A / B [ / D / Z1 / ... / Zn] Example (see 5.1.4, example 2): Porosity: VDG-P201 S/5/2/C. A collective note shall only be used for the mainly occuring porosity in the casting.
6.2 Notes for defined areas
7.
Notes for defined areas can be required by the load case or by a functional surface. For pore classes D1 to D4 and load case F notes for defined areas are necessary (see 5.1.1 and 5.1.2).
[1]
According to this specification the note shall have a local reference: Graphical sy mbol for porosity
stress type max. permissi ble porosi t y max. pore diameter addi tional parameters
References, standards, guidelines
DIN EN 1559-1 Founding – Technical Conditions of Delivery – Part 1: General. [1a] DIN EN 1559-4 Founding – Technical Conditions of Delivery – Part 4: Additional Requirements on Aluminium Alloy Castings. [1b] DIN EN 1559-5 Founding – Technical Conditions of Delivery – Part 5: Additional Requirements on Magnesium Alloy Castings. [1c] DIN EN 1559-6 Founding – Technical Conditions of Delivery – Part 6: Additional Requirements on Zinc Alloy Castings.
Example (see also examp le 3 in 5.1.4)
Near the title block of the drawing a reference to VDG specification P201 shall be given as necessary, using a collective note according to 6.1.
[2]
DIN EN 444 Non-destructive Testing, General Principles for the Radiographic Examination of Metallic Materials Using X-rays and Gamma-rays
[3]
DIN EN 12681 Founding – Radiographic Inspection
[4]
ASTM E 155-95 Standard Reference Radiographs for Inspection of Aluminium and Magnesium castings.
[5]
ASTM E 505 Standard Reference Radiographs for Inspection of Aluminium and Magnesium Die Casting.
[6]
DIN EN 583-1 Non-Destructive Tests – Ultrasonic Examination – Part 1: General Principles
[7]
DIN EN 1593 Non-Destructive Tests - Leak Tightness Test – Bubble Emission Technique.
[8]
DIN EN 1779 Non-Destructive Tests – Leak Testing – Criteria for Method and Technique Selection.
[9]
ISO 10049
Page 9, VDG SpecificationP 201
Aluminium Alloy Castings; Visual Method for Assessing the Porosity. [10] ISO 3058 Non-Destructive Testing – Aids to Visual Inspection – Selection of Low-Power Magnifiers [11] ISO 10135 Technical Drawings – Simplified Representation of Moulded, Cast and Forged Parts. [12] Sonsino, C. M.; Dietrich, K.: Einfluß der Porosität auf das Schwingfestigkeitsverhalten von Aluminium-Gußwerkstoffen. Fraunhofer-Institut für Betriebsfestigkeit (LBF) Darmstadt, AiF-Forschungsvorhaben Nr. 5899 (1990). [13] Ermittlung der Rißzähigkeit von Aluminium-Gußwerkstoffen an Kleinproben unter besonderer Berücksichtigung einer vergleichenden Auswertung unterschiedlicher fließbruchmechanischen Konzepte. Abschlußbericht zum AiFForschungsvorhaben Nr. 6048, Institut für Werkstofftechnik, Gießereikunde der TU Berlin, Berlin 1987. [14] Einfluß der Porosität bei Aluminiumgußlegierungen auf die Schwingfestigkeit unter Biegebelastung auf die Rißentstehung und den Rißfortschritt. Abschlußbericht des AiF-Vorhabens Nr. 8977, Darmstadt 1997. [15] Hück, M.; Naundorf, H.; Schütz, W.: Bruchmechanische Untersuchungen und Rißfortschrittsmessungen an lunkerbehafteten, bauteilähnlichen Proben aus GK-AlSi12. Z. Werkstofftechnik 14 (1983) p. 325-329. [16] Schindelbacher, G.: Einfluß unterschiedlicher Porosität auf die mechanischen Eigenschaften der Legierung GDAlSi9Cu3. Giesserei Praxis (1993) Nr. 19, p. 381-392. [17] Sonsino, C. M.; Ziese, J.: Schwingfestigkeit von Aluminiumlegierungen in verschiedenen Porositätszuständen und Aussagen zum Bauteilverhalten. VDI-
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Werkstofftagung März 1991.
91,
München,
4./5.
[18] Ostermann, H.: Schwingfestigkeit gekerbter Flachstäbe aus der Aluminiumlegierung. AICuMg 2 (3.1354.5) im Bereich zwischen 106 und 107 Lastspielen Fraunhofer-Institut für Betriebsfestigkeit (LBF), Darmstadt Technische Mitteilungen TM-Nr. 38/68 (1968) [19] Dieterich, K.: Schwingfestigkeit von höchstfestem Aluminiumguß. Fraunhofer-Institut für Betriebsfestigkeit (LBF) Darmstadt, LBF-Bericht Nr. 7543, AiFForschungsvorhaben-Nr.10449N (Mai 1999). [20] Pries, H.: Einsatz der quantitativen Bildanalyse zur Bestimmung der Porengehalte in Aluminium-Druckgußteilen. Vortrag auf dem 1. Internationalen Deutschen Druckgußtag in Neuss am 13. April 2001. [21] Pries, H.; Helmke, E: Einsatz der quantitativen Bildanalyse zur Bestimmung der Porengehalte in Aluminiumdruckgußteilen. Giesserei 88 (2001) Nr. 12, p. 49 – 55. [22] Mertz, Klein, Badwidamann: Druckgußfehler-Katalog Aluminium. [23] Schumacher, F.; Widmaier, T.: Druckgußfehler-Katalog Zink. [24] Rudat, M.: Magnesium.
Druckguß
Fehlerkatalog
AiF-Forschungsvorhaben (research projects of the German Federation of Industrial Cooperative Research Associations) can be obtained from the VDG information centre. Druckguß-Fehlerkataloge (casting defect catalogues) can be obtained from the Steinbeis Transferzentrum, Arbeitsgemeinschaft Metallguss at Fachhochschule Aalen (Prof. Dr. F. Klein), Gartenstr. 131, 73430 Aalen, Germany.
Annex 1 Definition of further flaws A 1.1 Cold flow marks Cold flow marks are patterns representing the borders of different feeding flows on the casting surface.
A 1.2 Stick marks These are depressions on the casting surface created when one or several thin layers fused with the mould surface are torn out. They often occur in areas which are extremely heated during the mould filling process.
A 1.3 Draw marks Draw marks result from local material removal and look like score marks and scratches on the casting surface parallel to the direction of mould separation. They are caused by friction between the materials when the casting is removed from the mould and when the core is drawn.
punching, milling, drilling etc. Casting burrs are thin-walled material accumulations and metal residues adhering to the casting which result from penetration of the melt in the mould parting line or in fitting gaps of mould inserts or cores during casting.
A 1.5 Hot cracks Hot cracks have a cobweb-like, raised structure on the casting surface. They result from permanent damage of the die in the form of cracks. These cracks mainly occur in areas of high temperature cycle stress during casting.
A 1.6 Further characteristics of cast components Dimensional deviation, incomplete mould filling, volume variation, distortion, inclusions, ejection marks, flow lines, sink marks, lakes, forced cracks and spotted surface are further characteristics of castings. In this context reference is made to the corresponding literature [22 to 24].
A 1.4 Burrs Burrs include casting burrs and burrs resulting from the deformation of material during
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Annex 2
Microstructure examples of pore classes 0, 4 and 8 Pore surface area
8%
4%
Density
Pore class
0%
Figures taken fromBilder [12] Bilder ausaus [12][6]
Figure A.2.1 Microstructures and fracture structures in the starter crack area of casting alloy GAlSi7Mg0.6 wa [12]
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Annex 3 Examples of different porosity in general and in dependence on the reference surfaces (informative) The microsections are taken from components with different requirements These components have met the requirements set for them.
For Figures A.3.1 to A.3.4 porosity is specified for the entire area. Figures A.3.5 and A.3.6 contain reference surfaces with porosity specifications analogous to Figure 2. In some figures possible reference surfaces are indicated.
Figure A.3.2
Figure A.3.1
Aluminium die casting, round gas pores, porosity 1 %
Aluminium die casting, porosity 3 %
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revised and updated 2002-10-16
Figure A.3.3 Aluminium die casting, milled specimen, shrinkage cavities, porosity 2 % (cavities in joint area)
Porosity in small square: 9 % Porosity in large square: 4 %
Figure A.3.4 Zinc die porosity 7 %
Porosity in small square: 1 % Porosity in large square: 12 % Porosity in dashed square: approx. 30 %
3
casting,
Note on Figure A.3.6 The dashed square makes clear the necessity of choosing an area for measurements which is small enough to cover the relevant area. At the same time, it has to be large enough to properly represent the pore distribution.
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Figure A.3.5 Reference surfaces for porosity specification (see 5.1.2), joint area
Figure A.3.63 Reference surfaces for porosity specification (see 5.1.2) (cf. Figure A.3.4)
It is planned to include all types of porosity occurring in non-ferrous metal castings in a catalogue of examples. This catalogue will contain figures which can be assigned to the different porosity classes according to this specification. The users of this specification are requested to provide such examples with specification of scale, porosity designation and requirements for the component to:
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VDG-Fachgruppe 2 NE-Metallguß, Sohnstraße 70, 40237 Düsseldorf, Germany. E-Mail:
[email protected]
revised and updated 2002-10-16
